This invention relates to a method of manufacturing a metal part having three petal-like arms extending from one end of a solid cylinder, such as a tulip-shaped component of a tri-port type constant velocity universal joint in an automobile drive shaft, by closed chamber extrusion of a cylindrical rod and an apparatus for performing this closed chamber extrusion method.
In tri-port type constant velocity universal joints for automobile drive shafts, which are employed chiefly in front-engine front wheel drive cars, an important component serving as a sort of yoke is a tulip-shaped part that has three petal-like prongs or arms extending from one end of a solid cylinder in a circumferentially equally spaced arrangement. In a root portion, the three arms extend obliquely outwardly with respect to the center axis of the solid cylinder, but in the remaining portion they extend parallel to the center axis of the cylinder. The axially extending portion of each arm has the shape of a part of a cylindrical wall and is larger in width than the root portion. The material of this tulip-shaped part is a high tensile steel such as a chromium-molybdenum steel. Because of the intricateness of the overall configuration and the difference in width and hence in sectional area between the root portion and the axially extending portion of each arm, this tulip-shaped part can hardly be manufactured by an ordinary forging method.
Usually, the tulip-shaped part is manufactured by initially shaping a metal plate into a bell-shaped rough form by hot forging and then cutting three axially elongate slots in the cylindrical wall of the bell-shaped workpiece at circumferentially equal distances by means of a milling cutter, for example as disclosed in U.S. Pat. No. 3,805,653. However, this process is time-consuming and suffers a considerable loss of material.
Japanese Patent Application Primary Publication No. 54(1979)-81150 proposes to manufacture the tulip-shaped part through the steps of initially forming three axial grooves on the periphery of a cylindrical material by means of an extrusion machine fitted with die inserts for grooving, then machining the inside of the grooved cylinder to obtain a roughly tulip-shaped part and finally machining the outer surfaces and tip portions of the three arms. This process requires many machining operations with a considerable loss of material and can hardly be expected to bring about an appreciable improvement in productivity. Moreover, the repeated machining operations will possibly be detrimental to the physical strength of the finished product.
British Patent No. 1,474,876 proposes to manufacture the tulip-shaped part by a multi-stage die forging process using differently designed dies at the respective stages, supplemented by a relatively simple machining step. Although the loss of material is reduced, this process is quite low in its rate of production.
Meanwhile, it has been proposed to manufacture metal parts of rather intricate shapes by a sort of die forging process, wherein a portion of a cylindrical material is extruded into a closed chamber of an elongate shape defined in an assembly of two die blocks, for example in Japanese Utility Model Application No. 43(1968)-30038. However, it is believed to be quite difficult to manufacture the above described tulip-shaped part by this forging-extruding method.